This invention relates to a leakless pump capable of detecting wear of its bearings for previously preventing troubles of its main members due to the wear of the bearings.
There have been leakless pumps constructed particularly for the purpose of transferring harmful chemical and medicinal liquids, expensive chemical liquids, high temperature liquids and the like. In general, these leakless pumps utilize sliding bearings or plane bearings incorporated therein. In this hitherto used leakless pumps, however, worn conditions of such bearings cannot be detected from the outside of the pumps. Accordingly, although bearings have worn off to an extent to be exchanged with new ones, they are often still used until a rotor is brought into contact with a casing to damage it resulting in leakage of a liquid.
In order to overcome such a disadvantage, for example, Japanese Laid-open Patent Application No. 50-54,903 discloses detecting means for detecting positional change of a rotor including an impeller with the aid of a magnet built in the rotor and a coil located near to the rotor. With a pump intermittently operated with repeating temperature rise and drop between the room temperature and 150.degree. C., however, the magnetic force of the magnet changes with the temperature variation in a range of the order of about 10%. The change in the magnetic force greatly afficts the magnetic field to make difficult the exact detection of the wear of bearings. In such a system, moreover, the positional change of the rotor is detected with the aid of electric voltage which is susceptible to external disturbance. Therefore, an exact detection of the bearing wear cannot be expected.